A power converter circuitry for converting a direct voltage of 1500 V into an alternating voltage is known from railway technology and from US 2005/284673 A1. For this purpose, several series-connected power converters are utilized, each power converter having a controllable bridging switch. Each bridging switch lies in a direct voltage intermediate circuit which bridges the respective one of the power converters when closed.
In wind power plants as they are described in EP 1 921 738 A2, a resistance chopper is connected in parallel with a full-bridge circuit of an inverter and with a capacitor in the direct voltage intermediate circuit. The direct voltage can be adapted by adding the chopper to the circuit.
The publication Calais M. et al, “Multilevel converters for single-phase grid connected photovoltaic systems: an overview”, Solar Energy, Pergamon Press. Oxford, GB, Bd. 66, Nr. 5, 1. August 1999, pages 325-335, xp 004362671, issn 0038-092x describes a photovoltaic plant with several strings. An inverter or a bridge circuit and a capacitor are associated with each string.
In order to allow for high efficiency and galvanic separation in a photovoltaic plant, the document EP 1 870 996 A1 teaches combining a resistance chopper connected to a direct voltage intermediate circuit with switching elements for switching transformer taps.
It is the object of the invention to improve a power converter circuitry of the type mentioned in such a manner that it is suited for photovoltaic generators and is highly efficient.